Off-axis electron holography of FIB-prepared semiconductor specimens with mV sensitivity

Abstract

Off-axis electron holography is a TEM based technique that uses a biprism to interfere an object wave that has passed through a specimen with a reference wave that has passed through only vacuum. From the interference pattern, or hologram, both phase and amplitude images can be reconstructed. In the absence of magnetic fields, the phase change, ΔΦ of an electron as it passes through a sample is given by the expression, $$ \Delta \Phi = C_E \int_0^t {V(x,y,z)dz ,} $$ where C E is a constant dependent on the energy of the electron wave, V is the electrostatic potential and z is the direction of the electron beam [1]. As the phase of an electron is very sensitive to changes in potential in a specimen, such as from the presence of dopants, electron holography can in principle be used to fulfil the requirements of the semiconductor industry for a technique that can be used to quantitatively map dopants with nm-scale resolution [2].